Connection part for aluminium cables

Abstract

A connection part for aluminium conductors comprising a substrate (6) formed as a connection piece (4), wherein the connection piece (4) is formed as a flat part with a rectangular cross-section or as a bolt, or the connection piece (4) is formed as a flat part with a rectangular cross-section and a bore, or the connection piece (4) is formed as a bolt with a bore, characterized in that the substrate (6) is formed from one of the aluminium alloys with an Rp0.2 value between 250 N / mm^2 and 470 N / mm^2 and is coated with at least one coating (14) of phosphorus-alloyed nickel NiPx, wherein X is between 5-15 percent by weight.

Description

The subject matter relates to a connection part for aluminum lines comprising a substrate formed as a connection part. The subject matter furthermore relates to a connection of such a connection part to an aluminum line and to the use of such a connection part and such a connection in a motor vehicle, in particular in an automobile.In particular in automotive applications, the number of aluminum lines, whether made of solid material or strands, whether round or flat, increases steadily. Compared to conventional copper lines, aluminum lines have a weight advantage with the same current carrying capacity. In addition, aluminum is considerably less expensive than copper. Thus, the cost pressure in the automotive application field can be met.Aluminum wires are mainly used as high current wires such as battery wires. However, control lines are increasingly formed from aluminum. The problem with aluminum lines, however, is that they must be electrically conductively connected to the vehicle electrical system and electronic system. Due to the chemical properties of aluminum, an aluminum oxide is formed on its surface, which acts as an insulator. Connections with lines made of other metals are moreover difficult to produce due to contact corrosion.Previous solutions propose welding contact tabs made of copper or copper alloys to the aluminum line. European patent application EP 1 032 077 A1, for example, discloses the connection of an aluminum line to a cable lug made of copper, an aluminum sleeve pressing the strands of the aluminum line.German patent application DE 10 2008 035 863 A1 discloses a motor vehicle conductor connection element in which an insert is arranged on the surface of a flat part made of aluminum. The insert serves for connecting the connection element to a further electrical contact element.DE 10 2010 027 082 A1 describes a clamping body for an electrical conductor having a clamping body pocket which forms a receiving space for receiving the electrical conductor. The clamping body has the properties of a clamping body produced from a brass-containing alloy.DE 10 2012 013 176 A1 relates to a tear-off screw for a device for screw-clamping electrical conductors, having a threaded section for screwing the tear-off screw into a terminal body, wherein the threaded section has, at least in sections, a thread having an unsymmetrical threaded profile.US 2011 / 0 194 974 A1 discloses an aluminum extrusion material for a connector formed of 0.2 to 0.8% by mass percent of Si, 0.45 to 0.9% of Mg, 1.0 to 3.5% of Zn, 0.001 to 0.2% of Ti, and inevitable impurities.DE102008035863A1 shows a motor vehicle conductor connection element having a first flat part and an insert arranged with a surface of the flat part substantially flush with the surface in the flat part. In order to ensure contacting with different conductors, the flat part 4 is substantially completely coated with a metal 12 and the insert 6 is partially coated with the metal 12.However, the combination of two different metals, in particular copper or copper alloys, with aluminum or aluminum alloys results in an increased corrosion potential at the contact point. In order to make the corrosion potential as low as possible, the connection along the seam between the metals is to be designed to be protected and, if appropriate, to be protected from environmental influences, in particular liquid and moisture.In particular in the case of a fusion welding process, care must additionally be taken, in the case of various metals, in particular aluminum and copper, to ensure that brittle Al 2 CU phases and intergranular corrosion are avoided as far as possible.Moreover, tinning in a tin bath, as is customary in copper contacts, is possible only with considerable outlay when using aluminum connectors. In particular in the case of a tin bath, it is important to ensure that the aluminum is initially freed from the aluminum oxide layer. This is considerably more complicated in terms of process engineering than in the case of copper-based materials and leads to high process costs.Proceeding from these disadvantages, the object was to provide a connection piece which, in addition to good transition resistances, withstands the mechanical requirements during assembly and the life cycle.This object is achieved by a connection part according to claim 1, a connection according to claim 9 and a use according to claim 12.During the life cycle of a connecting part with a connecting part, the latter is subjected to severe chemical and mechanical loads. A chemical load arises in particular in vehicle construction due to splash water, in particular in winter months. Such splash water may be mixed with scattering salt and may be highly corrosive.In order to counteract contact corrosion at a contact between an aluminum line and the connection part, it has been found that the substrate of the connection tab is preferably likewise formed from aluminum or an aluminum alloy, so that, on account of the material equality between the connection part and the line, the risk of corrosion is at least reduced, at best prevented. This is firstly disadvantageous because aluminum tends to flow under compressive stress. Force-fit connections, in particular screw connections made of aluminum, therefore tend to fail during the life cycle under mechanical loading.However, in order to meet the mechanical requirements of the assembly as well as during the life cycle of the connector, it has been found that a substrate having an Rp0.2value between 250 N / mm^2and 470 N / mm^2is still capable of withstanding the mechanical loads. This Rp0.2value is preferably determined according to DEN ISO 6892-1, ISO 6892. An Rp0.2value of at least 250N / mm 2, preferably at least 270N / mm 2, in particular more than 300N / mm 2 offers creep properties of the substrate, which also under mechanical loads enable a permanent force-fit connection, in particular a screw connection.In particular, the materials EN AW 2017A, EN AW 6056, EN AW 6082 and EN AW 7075 have proven to be suitable in accordance with the specifications of the international alloy register ("registration record of international alloy specifications and chemical composition limits for rolled aluminum and rolled aluminum alloys").With the selection of the multitude of different aluminum alloys, the inventors have surprisingly found that those aluminum alloys having one of the Rp0.2values mentioned, in particular the aluminum alloys mentioned, are particularly suitable for the mechanical stress of connection parts. In particular, these alloys can be readily screwed together and do not lead to the material not flowing desired under mechanical stress. Moreover, it has surprisingly been found that these alloys can additionally be coated particularly easily with electroless or electrochemical metallic coating, so that oxide-free, dense surfaces can be produced for welding on these alloys in particular.The said Rp0.2value and in particular the said four alloys from the multiplicity of possible alloys provide both mechanical and chemical properties which are particularly suitable in automobile construction. In addition to the mechanical strength, the surface of these materials is also suitable for being coated if required.The task of a coating is to prepare the substrate of the connecting tab connection piece for a welding process, in particular a friction welding process, a resistance welding process or an ultrasonic welding process. For this purpose, it is necessary to produce an oxide-free, dense surface. The alloys mentioned are particularly suitable for this purpose, since coating thereon is possible in a particularly simple and process-safe manner.The connector piece has a rectangular cross section according to an alternative. In particular in the connection between a flat conductor and the connection tab, wherein the flat conductor also has a rectangular cross section and is formed from solid material, the connection tab can likewise be formed from a rectangular cross section. In this connection, it should be mentioned that in the present application the term "flat conductor" or "line" is to be understood such that a conductor or a line represents the current-carrying part, the core, of a cable. A cable is formed of a conductor and an insulation.The connecting piece can also be formed as a bolt according to an alternative. This bolt can be welded directly onto an aluminum conductor, in particular a flat conductor, in particular on the end face. The bolt can also have a thread, in particular at an end face. A screw connection to a further contact piece can be effected via this.As already mentioned at the beginning, the connecting piece is particularly suitable since it satisfies the mechanical requirements during assembly and during the life cycle. During assembly, for example, screwing on a screw must be possible without these shearing off the thread. Also, the connecting piece must not flow under mechanical load, in particular by a screw or nut, due to the pressing force thereby brought about. Moreover, during operation, for example, a screw connection must remain stable and, in particular, it must withstand vibrations, temperature-related expansions of the material and bends of the connection part. The present connection piece offers all these advantages over other aluminum alloys.According to an alternative, the connecting piece has a bore. The bore can be formed as a through bore. It is also possible for the bore to be formed as a blind bore, in particular with an internal thread (bushing). It is also possible for a contact part, in particular a connection bolt, for example a threaded bolt, to be screwed to the connection piece. In this case, the contact part can be screwed directly to the connecting piece by providing a thread in the connecting piece or the bore. It is also possible for the contact part to be fastened to the connection piece via at least one nut.The coating of the connecting piece is intended to prevent a reaction, for example a diffusion, with the contact part from taking place in the connection region. For this purpose, it is necessary for the coating to have a dense surface. Besides the reaction with the contact part, it is necessary to prevent an aluminum oxide layer from forming on the aluminum, the formation of which is promoted by electrolytes.It has been found that a chemical, in particular electroless or electrolytic, coating with nickel meets these requirements in particular. By wet-chemical application of the nickel alloy to the connection piece or the substrate, at least in parts, it is possible to apply the coating directly to the material of the aluminum alloy, bypassing the oxide layer. The coating protects the substrate of the connection piece from direct contact with a contact part and thus from contact corrosion during joining to the contact part, in particular if it is formed from another metal, for example a copper alloy. During the coating, for example, the oxide layer can first be etched away. A zinc pickling agent can then be applied, in order to subsequently apply a nickel layer. A nickel phosphor layer, for example, can be deposited on this surface, which is then oxide-freeFor creating a particularly dense weldable surface, the use of a nickel-phosphorus alloy has proven to be advantageous. The nickel-phosphorus alloy is such that the phosphorus content is between 5 and 15%, in particular between 8 and 12%, percent by weight. This coating with the stated phosphorus content leads to a particularly dense surface.Possible ageing cracks in the coating can be counteracted by providing an additional tin coating. In particular, the tin coating takes place on a first coating, in particular on a first nickel coating. The coating is effected in particular in such a way that the tin layer is applied at least in parts to the nickel layer.It is not necessary that the entire substrate be coated. Rather, it is sufficient if a part of the substrate, in particular the part facing the contact part, is coated. It is also possible for a coating with the nickel alloy to completely coat at least one surface and for an additional tin alloy to take place only in parts.By coating with a tin layer on the nickel layer, capillary effects such as moisture bonds to the substrate due to cracks in the nickel layer are prevented.According to one exemplary embodiment, it is proposed that the connecting piece is welded to a flat part or a bolt. In particular, ultrasonic welding, friction welding, rotational friction welding or resistance butt welding can be used to weld the connection piece, in particular in the region of the coating, with a bolt. It is also possible that instead of a bolt, another contact part is welded to the connection piece in the area of the coating. The stated welding produces an intermetallic connection between the contact part, in particular the bolt and the coating. The coating thus serves as a weld preparation and the welding can take place directly on the coating.Turning off the friction welding contact of the contact part or the bolt is no longer necessary. Specifically in ultrasonic welding, the intermetallic connection takes place directly between the coating and the contact part, so that masking of the welding region during the coating is no longer necessary. It is not necessary to perform welding directly on the aluminum surface, which would necessitate masking.A further aspect is the connection of a described connection part to an aluminum line. The aluminum lead is preferably formed of E-aluminum. E-aluminium has good electrical properties since it is particularly pure. Purities of in particular more than 98%, preferably more than 99%, in particular more than 99.5%, have proven to be electrically advantageous. However, these aluminum alloys are not suitable for use as a terminal tab because they are mechanically too soft and not easy to coat.However, by connecting the connection part to the line, it is possible to produce an intermetallic contact of the connection part with a line which is of the same type. Contact corrosion is thus considerably reduced. In particular, welding can be carried out on the bare aluminum of the aluminum line to the bare aluminum of the connection part and an aluminum-aluminum connection is produced between the connection part and the aluminum line.The welding is preferably carried out by means of friction welding. The weld seam is thus preferably a friction weld seam.Aluminum lines can be formed from solid material and the welding can thus take place directly between the aluminum line and the connection part. If the aluminum line is formed as a stranded line, it may be necessary to mechanically fix the strands at their end face in order to enable the friction welding process. For this purpose, it is possible, for example, to fix, in particular compact, the strands by means of a sleeve and to weld the strand together with the sleeve to the connection part. The sleeve is preferably made of the same material as the strands.The connection between the connection part and the aluminum line is preferably effected at the end face. In particular, an end side of the connection piece is connected to the aluminum line. In particular, the end-face end of the aluminum line is connected in a materially integral manner to an end-face of the connection piece. Preferably, the connection piece and the aluminum line, or the aluminum line together with a sleeve on the end face, have identical cross sections, so that no cross-sectional jumps occur at the connection point and a uniform current flow is to be expected.The connection parts according to the invention and the connections according to the invention can be used in particular in a motor vehicle. In particular, the subject connector is suitable for withstanding the mechanical loads in automobile construction and has sufficient strength to resist vibrations, which cannot be excluded in the motor vehicle, temperature-related expansions and bends over the life cycle.In particular, the connection parts or the connections can be used in battery lines which, due to the high current-carrying capacity, have to have large conductor cross sections. Particularly suitable are the starter battery line, the generator battery lines or the starter generator lines. Especially in these areas, particularly due to under-floor installation or even installation in the engine compartment, a high resistance to environmental influences is required, since splash water cannot be prevented in these areas.The subject matter is explained in more detail below with reference to a drawing showing exemplary embodiments. In the drawing, the following are shown: FIG. 1 a is a sectional view of a connection part; FIG. 1 bshows a top view of a connection part according to FIG. 1 a; FIG. 1 cshows a sectional view of a connection part with a screw as contact part; FIG. 1 dis a sectional view of a connection part with a screw and a nut as contact parts; FIG. 1e is a sectional view of two connecting parts with a threaded bolt; FIG. 2 is a view of a possible connector; FIG. 3 is a view of a possible connector; FIGS. 4a-c are sectional views of coated connectors; FIGS. 5a-d are sectional views of partially coated connectors; FIG. 6 a shows a sectional view of a first connection according to an exemplary embodiment; FIG. 6 bshows a sectional view of a second connection according to an exemplary embodiment; FIG. 7 a is a view of a connection part with a bolt as a connection piece; FIG. 7 bshows a sectional view of the connection part according to FIG. 7 a.The connection parts in question are intended for aluminum lines.The connecting parts according to FIGS. 1 to 6 are formed as flat parts, the connecting part according to FIGS. 7a, b as bolts. The substrate of the connection piece has an Rp0.2value of more than 250N / mm 2 and is formed in particular from an aluminum alloy according to EN AW 2017A, EN AW 6056, EN AW 6082 or EN AW 7075. These alloys are described in the international alloy register ("registration record of international alloy specifications and chemical composition limits for rough aluminum and rough aluminum alloys"). These four alloys have been found to be particularly suitable under the selection of the variety of possible aluminum alloys. These alloys in particular are suitable for use in automotive fields both surface-chemically and mechanically.They have sufficient mechanical strength to withstand vibrations, temperature-related expansions and bends in automotive applications. Mechanical connections can also be produced with the connection part in question during assembly, in particular by screws, without the material of the substrate flowing in such a way that permanent fixing would not be possible. The aluminum alloys mentioned can furthermore be coated wet-chemically, electrolessly or electrolytically with a nickel layer, in particular with a nickel layer made of a nickel-phosphorus alloy.The shapes of the connecting pieces 4 shown in the figures are purely exemplary. It is essential that the connecting pieces 4 have an Rp0.2value of at least 250N / mm 2. They are preferably formed from the stated aluminum alloys.FIG. 1 ashows a connection part 2 which is formed as a flat part (connection tab) 4. The connection tab 4 is formed from a substrate 6. By way of example, a bore 7 is provided in the connection tab 4. This bore 7 is shown in the present case as a through bore, but can also be formed as a blind bore. An elongated hole bore is also possible.A plan view of the connection tab 4 according to FIG. 1 bshows that the bore 7 is formed on the connection tab 4 formed as a flat part.However, the connecting tab 4 can also be formed as a connecting bolt, as is illustrated in FIG. 2. In this case, the connection tab 4 has, for example, a round cross-sectional profile, whereas the connection tab 4 according to FIGS. 1 aand bhas a rectangular cross-sectional profile. The connecting bolt can also have a thread, for example, and can optionally be formed as a threaded rod.The connecting tab 4 can also be formed as a bent connecting part, as is illustrated in FIG. 3, in particular for special applications and for better weldability to lines.FIG. 1 cshows the screwing of the connection tab 4 with a screw 8, and it can be seen that a thread is provided in the bore 6, into which the screw 8 is screwed. By using the above-mentioned alloy as substrate 6, it is possible to provide the screw connection by means of screw 8. The substrate 6 has sufficient mechanical strength to be screwed.FIG. 1 d shows a further possibility of screwing. In this case, the screw 8 is screwed to the connecting tab 4 by a nut 10. The substrate 6 of the terminal tab 4 is suitable to resist and not flow the forces which the nut 10 and the screw 8 exert on the surface of the terminal tab 4, so that a permanent mechanical connection is possible.Screwing the connection tab 4 to a further contact part 12 via a screw 8 and a nut 10, as shown in FIG. 1 e, is likewise possible. The contact part 12 is preferably made of copper, in particular a tin-plated copper. In order to prevent contact corrosion, it is proposed that the connection part or the connection tab 4 is coated at least in parts.Such a coating is shown in Figures 4a-c and 5a-d. The coating can also be used in particular in the case of the compounds according to FIGS. 1 c- e. The coating prevents a phase boundary between aluminum and the coating from migrating under due to corrosion. In addition, a coating can provide a high-strength surface which is directly suitable for welding, in particular for ultrasonic welding, for friction welding or for resistance stump welding.FIG. 4 ashows the substrate 6 of the connection tab 4. a nickel-phosphorus layer 14 (nickel coating) is applied to the substrate 6 along at least one surface. The nickel-phosphorus layer 14 preferably has a phosphorus content of between 8 and 12%. In the figures, the coating is shown only on one side. It is understood that the coating as well as the multilayer coatings mentioned below can be carried out both partially and completely; in particular, a single or multilayer coating of the entire surface of the connection tab 4 can be carried out.It is also possible for a multilayer coating to take place. In this case, it is also possible, for example, to apply two nickel layers (nickel-phosphorus layers) one above the other, as is shown in FIG. 4 b. The substrate 6 is coated with a first nickel layer 14a and a second nickel layer 14b. The nickel layers are preferably formed from one and the same nickel alloy, preferably NiP x, with a phosphorus content of between 5 and 15%, in particular between 8 and 12%. The coating ensures that no aluminum oxide can form on this surface of the substrate 6 and that the contact resistance between the substrate 6 and a contact part, for example the screw 8, is kept low.A further multilayer layer system is shown in FIG. 4c. Here, a first nickel layer 14 ais applied on the substrate 6. A tin layer 16 is applied over it. The tin layer 16 seals the nickel layer 14a. Aging cracks in the nickel layer 14 aare sealed by the tin layer 16, so that capillary effects such as moisture bonding to the substrate 6 are prevented.FIGS. 5 ato d show a partial coating of the connection part 4.As can be seen in FIG. 5 a, a part of a surface of the connection tab 4 is coated with a nickel layer 14. The coating with the nickel layer 14 can be provided in a region in which the connection tab 4 is to be connected to a contact part 8. Welding can be effected directly on the surface of the coating, as will be explained below.FIG. 5 bshows a multilayer coating in which a first nickel layer 14 amelts the substrate 6 on one surface and a second nickel layer 14 bcoats the first nickel layer 14 ain part only. In the area of the coating 14b, particularly good weldability is given, since the thickness of the nickel layers 14a and 14b is sufficient that an intermetallic compound can be produced between a contact part and the nickel layers 14a and 14b without penetrating into the substrate 6.FIG. 5 cshows a further multilayer coating in which a first nickel layer 14 afully covers a surface of the substrate 6. A second layer may be a tin layer 16 that only partially covers the nickel layer 14 a. A surface section of the coating 14 acan be selected.FIG. 5 d shows a further partial coating in which a first nickel layer 14 ais already applied only in parts on the surface of the substrate and a tin layer 16 is applied on this first nickel layer 14 a.The various combinations of the coatings of Figures 4a to 4c and 5a to d may be combined. In particular, a first layer may be a nickel layer and a top layer, i.e. an upper coating, may be formed of either a tin or nickel alloy.The connection part 2 can be directly connected, in particular welded, to an aluminum line. This is shown in FIGS. 6 aand 6 b. FIG. 6 ashows a connection part 4 made of a substrate 6, the connection part 4 being partially coated with a first nickel layer 14 aand a tin layer 16 according to FIG. 5 c. At least one of the coatings 14 a, 16 may have been applied electrolessly or electrolytically. No aluminum oxide is formed between the coating 14a and the substrate 6, and the contact resistance between the layer 16 and the substrate 6 is nearly 0 ohm.A contact part 18, for example a copper contact tab, can be welded onto the layer 16. For this purpose, the contact part 18, which is formed from copper or a copper alloy, is placed with one end against the surface of the tin layer 16. The end of the contact part 18 to be welded can likewise be tin-plated. A weld joint 20 may be formed by ultrasonic welding, friction welding, or resistance butt welding, for example. An intermetallic compound is formed between the coating of the contact part 18 and the coating 16.In addition, the connection tab 4 can be directly connected to an aluminum line 22. The aluminum lead 22 is preferably formed of high purity aluminum and has excellent electrical properties. A weld 24 can be formed between the connection tab 4 and the aluminum conductor 22. This weld seam 24 can be effected by butt welding the end-face ends of the aluminum line 22 and the connection tab 4. A friction welding method is particularly suitable here. This welded connection 24 is an intermetallic compound which is of the same type, since both joining partners are formed from aluminum alloys. Contact corrosion is thus reduced to a minimum. The aluminum line 22 can be coated with an insulator 26 and thus be formed as an aluminum cable.A further possible connection is shown in FIG. 6 b. As shown in FIG. 4 b, the terminal tab 4 is coated with a double-layer nickel layer comprising a first nickel layer 14 aand a second nickel layer 14 b. A contact part 18, which is a connection bolt, can be butt-welded onto this nickel layer 14 b, for example. In this case, a flange of the contact part 18 can be placed on the end face of the nickel layer 14 band welded to the tin layer 14 b, for example by means of ultrasonic welding. The weld seam 20 is formed between the tin layer 14 and the material of the contact part 18, which is preferably a copper alloy. The end face of the flange can likewise be tin-plated, so that contact corrosion in this region is avoided.A cable made of aluminum strands 22 and an insulation 26 can be welded butt-ended to the connection tab 4. For this purpose, a sleeve 28 can be placed around the strands 22 and these can be compacted at their end-face ends. The weld seam 24 can then be formed by connecting the end-face end of the strands 22 to the connection tab 4 by means of, for example, friction welding. During friction welding according to FIGS. 6 aand 6 b, any aluminum oxide layer present on the connection tab 4 is broken open at the end side during friction welding, so that the contact resistance between the connection tab 4 and the line 22 is likewise low.FIG. 7a shows a view of a flat cable 30 with an insulation 26 and a core 32 formed from solid aluminum material. The bolt 34 has a thread at one end 34 aand is welded at the end face to the core 32 at another end 34 b.FIG. 7 bshows the bolt 34 with the cable 30 in section. It can be seen that the bolt 34 is preferably completely coated with a first layer 14 and a second layer 16, corresponding to the coating described above. The coating 14, 16 is broken open along the weld 40 during welding.Various combinations of the exemplary embodiments shown can be realized. The use of the substrates mentioned is advantageous in the field of automotive application and it has surprisingly been shown that the substrate claimed has specifically complied with the requirements in the automotive field.

Claims

Connection part for aluminium lines, comprising - a substrate (6) formed as a connection piece (4), wherein - the connection piece (4) is formed as a flat part with a rectangular cross section or as a bolt, or - the connection piece (4) is formed as a flat part with a rectangular cross section and a bore, or - the connection piece (4) is formed as a bolt with a bore, characterized in that the substrate (6) is formed from one of the aluminium alloys with an Rp0.2 value between 250 N / mm^2 and 470N / mm^2 and is coated with at least one coating (14) of phosphorus-alloyed nickel NiX, wherein X is between 5-15 percent by weight.Connection part according to Claim 1, characterized in that the substrate (6) is formed from one of the aluminium alloys EN AW 2017A, EN AW 6056, EN AW 6082 or EN AW 7075.Connection part according to one of the preceding claims, characterized in that the bolt has a thread, in particular in that the bolt has a thread at an end-face end.Connection part according to one of the preceding claims, characterized in that the bore is a through bore or a blind bore and / or a contact part (18), in particular a connection bolt, is screwed to the connection piece (4) and / or in that the connection piece formed as a bolt is connected to an aluminium line (22) in a materially integral manner, in particular in that an end face of the bolt of an aluminium line is connected in a materially integral manner.Connection part according to one of the preceding claims, characterized in that the connection part (4) is coated chemically, in particular electrolessly or electrolytically, in particular galvanically, at least in parts.Connection part according to one of the preceding claims, characterized in that the connection part (4) is coated at least in parts electrolessly with at least the phosphorus-alloyed nickel NiX layer, wherein X is between 8-12 percent by weight.Connection part according to one of the preceding claims, characterized in that the connection part (4) is coated at least in parts with at least one coating of tin (16), wherein in particular the tin layer (16) is applied to a nickel layer (14a, 14b).Connecting part according to one of the preceding claims, characterized in that the connecting part (4) is welded with a bolt (34) in the region of the coating, wherein the bolt (34) is connected at least to the coating (14) by intermetallic means, in particular by means of friction welding, resistance stump welding or ultrasonic welding.Connection of a connection part according to one of the preceding claims to an aluminium line (22), in particular made of E-aluminium, in particular with a purity of more than 98%, wherein the aluminium line (22) is welded to the connection part, wherein the weld seam is in particular a friction weld seam or ultrasonic weld seam.Connection according to claim 9, characterised in that the aluminium line (22) is formed from a solid material or as a stranded line.Connection according to claim 9, characterised in that the connection piece (4) is connected to the aluminium line (22) on the end face, in particular to an end face end of the aluminium line (22) in a materially bonded manner.Use of a connection part according to Claim 1 or a connection according to Claim 9 on a battery line, in particular on a starter battery line, a generator battery line, or a starter generator line, in a motor vehicle.

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